Oregon Spotted Frog

The Oregon spotted frog is an endangered species of frog native to the Pacific Northwest. It has a range spanning Canada and the United States, although most of the frogs no longer inhabit these regions due to their rarity. They have characteristic black spots with light centers and spend most of their time in the water.

Facts

• The Oregon spotted frog’s color varies with their age. They start off brown as spotless tadpoles with off white or cream underbellies and get spotted and redder as they grow older.
• Female Oregon spotted frogs are larger than the males. This has to do with their breeding responsibilities.
• The Oregon spotted frog is so rare that it has disappeared from 70 to 90% of its native range.
• Oregon spotted frogs have upturned eyes which enable them to see the surface activity from underwater.
• Oregon spotted frogs are the first species ever to be emergency-listed as endangered in Canada.
• Male Oregon spotted frogs make clicking sounds while floating on the surface of the water and even under it.

Scientific Name

The Oregon spotted frog is named after its appearance. It has black spots all over its body, including its head, legs, and back. The Oregon spotted frog is classified as Rana pretiosa, which means “precious frog,” which is pretty befitting considering its endangered state. It belongs to the genus Rana whose members are also called pond frogs, Holarctic true frogs, or brown frogs.

The Oregon spotted frog belongs to the family Ranidae whose members are called true frogs. They are characterized by their moist, smooth skin, muscular legs and webbed feet. Most of them are semiaquatic and have the widest distribution of all frog families.

Appearance

Oregon spotted frogs are “true frogs,” which means they are short-bodied, tailless amphibians with moist skin and short hind legs adapted for making strong, high leaps. The hind feet of Oregon spotted frogs are completely webbed as an adaptation to their semiaquatic life. They also have upturned eyes which stay that way even while they are in the water, allowing them to view what’s going on on the surface simultaneously.

The Oregon spotted frog’s color varies as they age. When they are tadpoles, they are mostly brown on top, off-white or aluminum-colored on their bellies, and they don’t have their notorious spots. When they are juveniles, they retain some of the brown color, but they can also be olive green. Their black spots with lighter centers start to appear at this time on their heads, backs, sides, and legs. Adult frogs become redder as they age and their colors range from brown to reddish brown, orange-red, to brick red. Their black spots also become larger, darker, and more ragged-edged as they grow older.

In terms of size, Oregon spotted frogs are about 1.75 to 4 inches in length from their snout to their vent and female frogs are larger than the male ones.

Evolution and History

Oregon spotted frogs belong to the class Amphibia which comprises of four-legged, cold-blooded animals that usually start out life as larvae in the water, though this doesn’t apply to all members of this class. Amphibians evolved from bony-limbed, lung-having sarcopterygian fish in the Devon period about 419.2 to 358.9 million years ago and adapted to terrestrial life.

Oregon spotted frogs belong to the order Anura, which houses tailless amphibians. The name Anura literally means “without tail” in Ancient Greek. Fossils of ancient frogs have been unearthed in every continent including the Antarctic Peninsula. Bits of the true frog started to appear in the Early Jurassic era.

An early frog fossil specimen called Prosalirus bitis was found in Arizona in 1995 and was dated all the way back to 199.6 to 175 million years ago. Prosalirus still had some of its tail, unlike modern frogs. Another frog specimen discovered from the Early Jurassic period is Vieraella herbsti, a now extinct true frog that bore a close resemblance to modern frogs and lived 188 million years ago. Important evolutionary milestones were reached 155 to 170 million years ago, when the frog species Notobatrachus degiustoi was alive. It had lost all of its tail and its body length had shortened.

Behavior

Oregon spotted frogs are semiaquatic, thus, they spend a lot of time in the water. Because of this, they always reside near a water body and would rarely be seen a far distance from one.

During the summer, Oregon spotted frogs are mostly inactive, but they stay very active during the winter when they are in the water. Naturally, the ideal water body for them would be one which is highly aerobic and does not freeze all the way down to the bottom.

Oregon spotted frogs return to the same place every year in order to reproduce. They breed in shallow water with enough sunlight and little to no shading from vegetation.

Habitat and Population

Oregon spotted frogs are native to the Pacific Northwestern region of the United States and Canada. They are located in British Columbia, Canada, down to the Puget/Williamette Valley, Washington, and Oregon.
Oregon spotted frogs are aquatic creatures and prefer warm wetlands, lakes, streams, and ponds. They inhabit areas with a still water source with sufficient shallow water and aquatic vegetation such as algae. The frogs use floating vegetation for basking in the sun and to hide away from predators.
Oregon spotted frogs live in different altitudes depending on their geographical location. Their desired altitude range is 65.6 to 5,151 feet above sea level.
The Oregon spotted frog is very rare. It is the most endangered frog species in Canada. They have disappeared from 70 to 90% of their range. Today, Oregon spotted frogs exist in just 33 populations that we know of and 20 of those are in Oregon.

The Oregon spotted frog is currently listed as a vulnerable species on the IUCN Red List of Threatened Species with a decreasing population.

Diet

Oregon spotted frogs like to sit still and wait for unsuspecting prey to show up before getting snatched up by their sticky tongue.

The adult Oregon spotted frog diet is mostly made up of insects such as flies and beetles, spiders, and water striders. Oregon spotted frog tadpoles indulge in algae, decaying vegetation, and detritus.

Predators and Threats

The Oregon spotted frog is officially a vulnerable species. It has also been listed as threatened under the Endangered Species Act and is the most endangered frog in Canada. In addition to this, its population has also been on the decline.

There are many factors linked to the downward spiral of the Oregon spotted frog population. Some of these factors include invasive predators, habitat loss, and other human activities.

Invasive Predators and Climate Change

The Oregon spotted frog is heavily preyed upon by invasive predators such as the Eastern bullfrog which preys on juvenile and adult Oregon spotted frogs, and the bass which eats tadpoles and frogs alike.

Climate change could affect the spotted frog even more by attracting the invasive predators to their habitats. Eastern bullfrogs are adversely affected by the colder weather of the spotted frog’s habitat, so warmer weather would favor the predator. A warmer climate could also result in the drying up of shallow water bodies which would greatly impact the spotted frog’s reproductive cycle.

Habitat Loss

Oregon spotted frogs are semiaquatic and need to reside near bodies of water. Human activities deplete the natural resources necessary for the survival of these frogs, such as damming, draining, encroachment, and overgrazing by livestock which destroys the shallow wetlands.

Invasive Plant Species

The Oregon spotted frog relies on aquatic vegetation for its daily living, as well as breeding and reproduction. Tadpoles mostly eat algae and decaying vegetation, so invasive plant species would naturally harm the frog’s ecosystem. Plant species like reed canary grass oust the native plants and cause an upset in the lives and well-being of the Oregon spotted frogs.

Fungal Disease

Chytridiomycosis is linked to the decline of hundreds of frog populations. It is caused by the spores of the Chytrid fungus which is released by waterborne pathogens. These pathogens can be carried by frogs to new locations, thus, spreading the disease. This disease is fatal to frogs and has affected 30% of the world’s amphibian population.

Firstly, the male frogs call out to the females from the location where they lay their eggs together in piles. Female Oregon spotted frogs breed each year in warm, shallow water two to twelve inches deep where underwater vegetation usually occurs. The female frogs lay their eggs in shallow water with enough sunlight so that the warmth would expedite the hatching process. They are known to produce one mass of eggs annually. Although each female lays one mass of eggs, they collectively deposit them in clusters at the same site. These communal sites can contain anything between 10 to 75 egg clusters.

The fertilized eggs turn into larvae and then hatch into tadpoles after 18 to 30 days. Their rate of metamorphosis depends on their location. In British Columbia, the tadpoles metamorphose to juvenile frogs after 110 to 130 days, and just after about 95 days in Oregon.

Female Oregon spotted frogs are not particularly maternal and will not guard or feed their offspring. Juvenile Oregon spotted frogs reach sexual maturity at two years of age if they are male and two or three years of age if they are female.

Due to their rarity and endangered status, some of the details about the reproductive life of Oregon spotted frogs remain unknown, such as their lifespan. It is generally believed that these frogs live up to two to five years old.

Reproduction and Lifespan

Oregon spotted frogs are communal breeders, which means that the females typically deposit their eggs at the same site, although some lone clusters have been observed. The breeding season for these frogs typically occurs between February and March and reproduction takes place in water. Exact breeding times may vary depending on the location, the water temperatures, and the elevation. Optimal breeding water temperatures for the Oregon spotted frog is around 46.4 degrees Fahrenheit. For regions of lower elevation such as lowlands, the breeding takes place from late February to early March, but for regions of higher elevation, this time shifts to late May to late June.

Related Animals…

• Bullfrog
• Goliath Frog
• Poison Dart Frog

1. Center for Biological Diversity, Available here: https://www.biologicaldiversity.org/species/amphibians/Oregon_spotted_frog/index.html
2. Oregon Zoo, Available here: https://www.oregonzoo.org/conserve/species-recovery-and-conservation/oregon-spotted-frogs
3. Pacific Forest Trust, Available here: https://www.pacificforest.org/species/oregon-spotted-frog/
4. Washington Department of Fish and Wildlife, Available here: https://wdfw.wa.gov/species-habitats/species/rana-pretiosa#conservation
5. Wikipedia, Available here: https://en.wikipedia.org/wiki/Oregon_spotted_frog